GB2253662A - Limited slip differential mechanism whose planet axes are rotatable - Google Patents

Abstract

Limited slip differential, e.g. for vehicle transmissions, has a carrier (18) rotating about a first axis in a support casing (12) typically driven by a crown wheel (22) and main drive pinion (24). A pair of output half shafts (14, 16) on said axis have output pinions (28, 30) within the carrier meshing with at least one, and preferably a pair, of planet pinions (32, 24) journalled in the carrier on a second axis normal to first axis to allow differential motion of the output shafts while transmitting drive to both from the rotating carrier in known manner. Controlled shifting of the planet gear(s) relative to the carrier by angular displacement of the second axis in a diametral plane of the first axis from a neutral position to an inhibiting position, e.g. by displacement of a planet gear shaft (36) in slots (38) of the carrier, when the carrier is subjected to drive torque brings formations, e.g. end faces (42, 44) of the planet gears, into braking engagement with formations (46, 48) of the carrier so as to inhibit the differential action. <IMAGE>

Description

2 2 5 - 6,3 2 1 PI C H A IN 1 5 DIFI C-RLENITIAL 1 C'"i This invention

relates to differential filect-janisr,-is as used in the drive transmissions of land vehicles and is more specifically concerned with limited slip differential mechanisms incorporating provision for automatically inhibiting the differential action if conditions arise in which there is substantial inequality of effective driving torque at the two driven output shafts or other driven outputs of the filechanism e.g. when wii--el spin would otherwise tend to occur.

jui;i-3rous proposals have been put forward for meeti this requireiment ranging frorf; basic operator-controlled devices for selectively locking the differential or rotation of the slippine, wheel independently of the other wheels, to more complex devices intended to operate automatically. Some examples of the latter forms of device are described in GB 878077, G3) 924805, GB 924863, GB 925176, and EP 0016541 hut these have riot always proved successful and dcceptahle in practice and some of tl'ier,.i are complex arid costly to manufacture., ant-' The object of the invention is to provide a ilif',':'t3reritial ii. iechaiiistii having, automatic limited slip operation which is simple in cons truc tion, durable arid reliable in use, and effective in providing the desired results.

According to tile invention there is provided a limited slip differential mechanism including a casing or other supporting formation, a carrier journalled on or in said formation for operatively driven rotation about a first axis, a pair of driven output elements each journalled for independent rotation about said first axis. arid at least one planet gear journalled in the carrier for rotation therewith and itself rotatable about a second axis normal to the first axis, said planet gear being meshed with both output elements to transmit drive thereto in common from the carrier while permitting 2 differential r-,lotion of the output elements relative to each other characterised in that said planet cear can shift relative to the carrier by angular displacement, the second axis relative to the carrier in a diamietral plane of 'the first axis between a neutral position at which the planet gear can rotate freely in providing said differential motion and an inhibiting position at which rotation of said gear is resisted or prevented by direct or indirect coaction between the planet gear and a braKing or stop formation of or on the carrier whereby the differential motion is inhibited automatically as a function of the transmitted drivino force transinitted through the carrier.

Preferably there will be a pair of said planet ge-:irs disposed to mesh with diametrally opposite sides of botli output elements so that they rotate in opposite directions under the differential motion and ---. :)nvt:!n-ieritly. but not essentially,, both planet gears will bj displaceable as referred to above. between neutral and inhibiting positions. Conveniently they will both be - gear shaft located in the carried on a comri-ion planet carrier. the shaft itself together with the planet gears being an-nularly displaceable as aforesaid.

the asseffibly will include provision for ad-justabld preloading of the planet gear or tlL,.,ars to j J provide predetermined resistance to its or their rotation about tha, second axis at the inhibiting position.

Preferably the inhibition of differential action is by a progressive braking effect through frictional enuagei,.ient with said coacting formation without locRing the planet gear(s) solid which could cause excessive stressino and consequent damage to components of the mechanism. It is desirable that the gear or gears are resiliently preloaded as aforesaid.

c xarziiples of the invention are now more particularly described with reference to the accompanying drawings, wherein..-- - i c j ure 1 is a cross section of a vehicle final unit incorporating differential iri-jchanist-,i of the invention ' Figure 2 is a detail on an enlarg i ied scale showinu the location of planet gears of the imechanism. Figures 3 Ja and 3b are end views in the direction of arrows 3-3 on r-itjure 2, and t:igures 4 and 5 are sectional d,..--,tails of modified planet gear arrangements.

0 Referring firstly to Finure 1 the final drive unit 1C1 shown by -.jay of example is a land vehicle axle unit C conventional layout havin-,,j an axle casit.il.-j 12 1 part only shown) locating a pair of half shafts 14,15 on 3 First axis which will drive near and oFfside road wheuls (noL shown) in the usual wily.

Th2 inner unds of shafts 14, 16 are received in a codx-Sally rotating carrier 18 journalled on bedrings 20 in casinc 12. The carrier r;irurits a crown wheel 22-, meshing with a main drive input pinion 24 also journallec.; in casing 12 so that the carrier is operatively rota-Lal-)ly driven about the first ixis.

mechanism 'erlerally as acts between half shafts 14,16 within and cdrried by the c a r r le r 1 UC The inner end of edch said shaf t mounts respective drive output elerient in the forri) ot en outputt, pinion 2c-i30. These pinions are spaced axially aPdrL in facing relationship and are located against axial outward thrust by bearing surfaces of carrier 18, the shafts 14,15 having splined engagement with them.

ile-shing with both pinions 2830 at diametrally opposite positions are a pair of planet pinions 32,34 located on a common second axis normal to the first axis of rotation of shafts 14,16 and carrier 18. Pinions 32,, 34 are located by and are rotatable on a comr-non planet gear shaft 36 which is in turn located in carrier 18 in the manner described in greater detail below.

As thus far described planet pinions 32,34 act in 4 conventional manner to permit differential relatlive r.notion or- the two output pinions 23,313 and their road wheels as when the vehicle is cornerinclwhile transmitting drive from the rotatably driven carrier 10 to both output pinions 2U7,3U in cor-.icnon.

The construction and mounting of the planet pinions and related components of the triechanism 26 is shown in Figures 2 and 3. The outer ends of the near shaft 33 locate in slots 38 defined by the carrier 108. The slots are elonuated in the direction of rotation of the carrier so that s-aici' shaft and the two planet pinions cc4n shift in d plane of the second axis normal to thu First axis from a neutral position shown in r-it,urezs a,, i, j 3b where Ithe shaft is centred in the slots 38 to dn -Ing position shown in Figure 3a in which the -ricis inhibit p 4- ol the shaft are displaced touards the ends of the.jlots. Shaft 3-6 is located against axidl disiila.ce;-.ient fror.n trit carrier 11)...)y a cross pin 40 erlrjagirig a through nore near one end of the shaft, said pin running longitudinally uf the related slot 38 so that it does not prevent said Thd aixially outer faces 42,, 44 of pinions have., in outwardly convex pdrt-split..ricai forin and the aujact,,fit inner of the portions of the carrier 16;jrourid thd slots 5G have a generally compleirinentary shape forneL: as concave part- spherical surfaces 43,48. The latter surfaces constitute coactinc formations of the carri,Zr providing the inhibition of differential action referred to below.

The erld faces 442,44 are preferably provided with donied braking pads 50 of high friction material.

Pinions 32,34 can shift axially on shaft 36 and they are pre-loaded axially outwardly of each other by an adjustable resilient sleeve assembly 52 best seen in detail in Figure 2.

Said assembly is located on shaft 36 between tile axially inner end faces of pinions 32,34 and comprises a sbc;jc!L., of dished resilient spring or Belville, washers 54 a sj,-.cer sleeve 56. an adjustable compression sleeve '58 hj-vi.rii,., inner and outer parts in screw threaded entiagement for selective adjustment of its effective axial length,, secured by a lock nut against displacement orice adjusted. and annular inner brake pads 60, S1 of high friction material which bear respectively against the inner end faces oF pinions 34 and 32 in opposite directions.

On assemlily the sleeve assembly 52 is adjusted to Lhe pair provide predetermined resilient pre-loading of 1. Of pi[liOns 32,34 axially outwardly of each other.

Any axiAl adjustment Of the Out-Put Pil-'i01-1s to ensure correct mashing with planet pinions -214 will. be achieved on assembly bY insertino spacer st.i netween the dxially outer faces of pinions 26,30 and the cdl.rier 10.

Tht-, radiii ori which the part--- sphe rical surfjcLs respective to the pinions 32,34 and the carrier formations 46.46 are struck are blightly different so ,,.[-ien shaFt 36 is anoularly displaced towards the inhib; ti 1-1l a Figure 3a (or clisplactr-.'..

j Position indic ted in r in the opposite direction frorn the neutral position i.e. to the right rcither than the lef t as viewed in Figures J whic'n also constitutes an inhibiting condition) the tti.,o Pinions.12.34 will he axially compressed on shaft 36 providling a braking force to substantially inhibit planetpinion rotation arid thus inhihit differential motion between the output pinions 283,30. The greater the angular displacement of shaft 35 the greater the inhibiting force though as said force is applied resiliently through the medium of the spring washers 54. and as the angular displacement of shaft 36 is limited by the length of slots 38, the arrangement is such that progressive force is never sufficient to completely lock the differential mechanism.

The drive torque applied through carrier 16 as it rotates in the direction of arrow 63 (Figure 3a) causes the outer ends of shaft 36 and hence pinions 32,34 to lag relaitive to said direction of rotattion so providing saic.' inhibiting action. If the vehicle corners, the faster rota-Lion of the road wheel which is outermost an the corner will urge the shaft 36 back towards the neutral position as the output pinion associated with said rodd wheel tends to overtake the rotational speed of carrier 18 so that the differential motion necessary for free turning (which is, in any case, usually needed under conditions of low driving torque) is maintained. The greater the applied drive torque the greater the inhibiting effect so resisting or substantially firc-venting wheel. spin.

It wIll lie rioted that the braking effect actint.. in pinionb 34 is applied to them in an axial inujard ' direction by. in effect. squeezing therin together in codction with the opposing carrier surfaces 46,48. Al-su axidl translation of said pinions relative to the carrier and the output pinions 26.30 is very small. This is in contrast to some proposed limited-slip differential rilechanisi.,is in which axial braking or shifting forces ar-- applied to pinions of the assef-,iljl.y in directions or to an exLent itinich c,-iri cause un(-iesirabt3 gear meshing stresst and consequent wear and risk of failure. Such irrariie.,r,ents r..iay also necessitate substantial reirife.rc--f!,.e,iit of the carrier arid/or dxle casing to L,jittist,:iri-1 the braking forces involved and/or specially shaued cCisiiiz.s drid comuonents to accommodate the unal rnechanism.

- L, - It will be appreciated that various arranger-nents of interacting faces or other formations of or associated with the planet pinions and the carrier could be provided for inhibiting the, differential motion on the angular displacement of the planet pinion axis relative to the carrier. Two possible alternative arrangements are illustrated diagrammatically in Figures 4 and 5.

IF) Figure 4 the outer end of the planet gear shaft 36 is located in a wedge-shaped insert 70 receive movably within a complementary taper-faced seating of the carrier 10. An axially inner face of insert 70 coacts with the 7 aXidily Outer face of the related planet pinion 34. As J 1 shaft 3G is displaced angularly along the direction of carrier rotation insert 70 will be carnmed inwardly to provide an axial braking force on the planet pinions.

Jigure 5 shows a similar arrangement except that an insert 72 in which the end of shaft 3ES locates as before coac--.ts uith the main part of carrier 18 to urge a male coned braking formation 74 axially into braking with a complementary female coned braking. Face, 7,3 in tti,,, outer end of associated pinion 34.

invention cdri be applliecl to standard sizes and fj.--ttLriis of diflerential axl-- or transwiission units with, littlz3 i.iorjific2.tiori oF the size and slidpe of their main so presenting ed-se of iiiterclidngeatiility Cind econar,iy of rtianufacture and fitting.

S

Claims (1)

1. A limited slip differential mechanism including a supporting formation, a carrier journalled on or in said formation for operatively driven rotation about a first axis, a pair of driven output elements each journalled for independent rotation about said first axis, and at least one Dlanet gear journalled in the carrier for rotation therewith and itself rotatable about a second axis normal to the first axis, said planet gear being meshed with both output elements to transmit drive thereto in common from the carrier while permitting differential motion of the output elements relative to each other: characterised in that said planet gear.can C shift relative to the carrier by angular displacement of the second axis relative to the carrier in a plane normal to the first axis between a neutral position at which the planet gear can rotate freely in providing said differential motion and an inhibiting position at which rotation of said gear is resisted or prevented by direct 0 or indirect coaction between the planet gear and a 0 braking or stop formation of or on the carrier whereby the differential motion is inhibited automatically as a function of the transmitted driving force transmitted through the carrier.

0 2. A mechanism as in Claim 1 including a pair of said planet -,ears disposed to mesh with diametrally opposite sides of both OUtDUt elements so that they rotate in opposite directions under the differential motion.

3. A mechanism as in Claim 2 wherein each said planet gear is displaceable between neutral and inhibiting positions.

4. A mechanism as in Claim 3 wherein the planet gears are both carried on a common planet gear shaft located in the carrier, the shaft itself together with the planet gears being angularly displaceable between neutral and inhibiting positions.

01 5.,iechinisi-,i as in any preceding, claiin includin,, provision for adjustable preloading of the planet gear or 0 ,ears to provide predetermined resistance to its or Gieir rotation about the second axis at the inhibiting position.

6. A;-,,eciianisi...i as in ClaL-ii 5 wherein said preloadin.g is resilient.

7. A. -ie---1iinispi as in Clai,-.,i 5 or 6 so far as dependent on Clain 4 wherein the planet ge-ars are displaceable relative to eac'ii other along the second axis, said 0 preloadin- bein- effected by z-.i preloadinassernibly locatell 011 the planet,,ear shaft to ur,,,,e said Sears apart 0 13 0 fro.-,i each other.

11 A,ecliianisr..i as in Claim 7 wherein the 1)reloa(lin,. assembly includes spring weans, a compression sleeve selectively adjustable in effective len-th, and brake 0 pads of friction material acting on the planet ears.

91.., -,eciiaiiisn as in any preceding claim in which said inhibition of differential. motion is i)ro-ressively effected by frictional en-a-ement with said fornation of or. on the carrier on displaceinent of the or ciic'-i planet gear to the inhibitiny position.

10. A..,iec2'iaiiisi-.1 as in Claim 9 wherein the carrier has braking, formation for frictional engagement ---ith a 0 0 complementary surface of the or each planet gear at the inhibiting position.

A, A,iechanism as in Claim 10 wherein said for,.-,iation or surface includes a facing of high friction braking iaaterial.

12. A rflechanism as in Claim 10 or 11 wherein the braking forr-iiation and complementary surface are part-spherical in,shape and so radiussed that the angular displacement of the second axis causes said progressive inhibition.

(0 13. A mechanisn as in Clai.,...1 10 or 11 wherein the brzi'.-iii., formnation of the carrier is a wedge shaped -insert seate-7 in a taper seatin.. and having a face in coactint,' relationship to the cor.iple-, ientary surface of the or eac'.] planet gear whereby displacement of Gae second axis to the inhibiting position cams said insert into progressive engagerment with tile respective planet gear.

14. "' iiccl-l anis.m as in any one of Claims 9 to 13 wherein an3ular displacement of the second axis Ibeyond a 1)re(IL-teri-,iried inhiDiting position is positively preventer, to ii-..,.iit the Ibraking en-agement so that the planet jear > W j or:,,ears are not cor.ipletely locc(d.

15. A..iec,iaiiisi.,.i as in any cclaim wherein I'ie- second avis can be displaced in either direction in said diametral plane from a median. neutral position so that said inhibition of differential tiotion will take place IrLvc 1 on cl -, of the carrier in either direction of rotation.

1 CJ A li.iiited slip differential niechanism substantially as Tiereinbeflore described wit,l reference to ancis as in '-r'i!,,ires 1,2 and 3, or those fi-ures as i. lodified by úi.,,,,iire A or Figure 5 of the -icr-o-.ipaiiyin7, drawings.

0 cl